Terahertz device integrated antenna for use in resonant and non-resonant modes and method

ABSTRACT

An assembly includes a device for receiving at least one input to produce an output. An antenna supports the device to transfer the input to the device and further to transfer the output from the device such that the antenna supports a selected one of the input and the output as a high frequency current. The antenna includes a peripheral configuration which confines high frequency current to at least one dominant path to oscillate therein. The other one of the input and the output is a lower frequency signal present at least generally throughout the antenna. At least one port is positioned away from the dominant path to isolate the lower frequency signal from high frequency current in the dominant path. The antenna is configured to support the lower frequency signal having a frequency in a low frequency range including zero to several terahertz.

RELATED APPLICATION

[0001] The present application is a Continuation in Part of U.S. patentapplication Ser. No. 09/860,988, entitled METAL-OXIDE ELECTRON TUNNELINGDEVICE FOR SOLAR ENERGY CONVERSION, filed on May 21, 2001 which isincorporated herein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] The United States Government has rights in this inventionpursuant to a contract awarded by a U.S. intelligency communityorganization.

BACKGROUND OF THE INVENTION

[0003] The present invention relates generally to arrangements forreceiving and emanating electromagnetic signals and, more particularly,to a device integrated antenna arrangement which is usable in resonantand non-resonant modes.

[0004] Recent energy crises have highlighted the growing demands placedon traditional sources of power, such as gas and electricity. Withrising energy costs, it is desirable to find alternative power sourcesto augment traditional power sources such as hydroelectric andthermonuclear. Solar energy conversion provides such an alternative bytapping into the readily available power of the sun.

[0005] One of the main obstacles preventing the proliferation of solarenergy conversion systems is efficiency. Currently availablesemiconductor solar cell systems are not able to provide the amount ofpower for the dollar that is possible by traditional power sources.Especially semiconductor solar cells with high energy conversionefficiency (ratio of incident solar power to electrical power out) areexpensive. Most solar cell systems are based on semiconductortechnology, which can be difficult to scale to the size required forlarge solar panels. Using the present technology, it is expensive tofabricate a semiconductor-based solar panel which is large enough toreplace the traditional sources of power. Moreover, semiconductordevices are generally single bandgap energy devices. This characteristicof semiconductor devices means that no current is produced when a photonhaving energy less than the bandgap energy is incident on thesemiconductor device and, when a photon having energy greater than thebandgap energy is incident on the semiconductor device, only currentcorresponding to the bandgap energy is produced in the semiconductordevice. In other words, the response of the semiconductor device islimited by the bandgap energy. Thus, the semiconductor device does notrespond at all to photons having energy less than the bandgap energy,and incident electromagnetic energy in excess of the bandgap energy iswasted in the energy conversion. Therefore, the energy conversionefficiency of the semiconductor device is low, on the order of 25% orless. Therefore, it would be desirable to achieve effective solar energyconversion using materials other than semiconductors.

[0006] One possible alternative to semiconductors is the use of ametal-insulator-metal (MIM) configuration The MIM configuration isrelatively inexpensive to manufacture in comparison tosemiconductor-based systems. The native oxides of the metals aregenerally used as the insulator materials, therefore the MIMconfiguration is straightforward to fabricate. Efforts have been madeeven as recently as 1998 (See Ref. 6) to improve the characteristics ofMIM devices, without substantially modifying the basic MIMconfiguration. Recent research in this area include efforts to use theMIM configuration to potentially provide devices capable of detectingand mixing signals at optical frequencies at optical communicationswavelengths.

[0007] Turning now to the drawings, wherein like components areindicated by like reference numbers throughout the various figures,attention is immediately directed to FIGS. 1A-1E. FIGS. 1A-1E illustratethe operation of an MIM device for reference purposes. As a simplifiedconfiguration, an MIM device is illustrated in FIG. 1A. The MIM device,generally indicated by reference number 10, includes first and secondmetal layers 12 and 14, respectively, with an insulator layer 16positioned therebetween. A corresponding energy band profile 20 is shownin FIG. 1B. Energy band profile 20 represents height of the Fermi levelin the metals and the height of the conduction band edge in theinsulator (y-axis 22) as a function of distance (x-axis 24) through MIMdevice 10 in the absence of provided voltage across the device. FIG. 1Cillustrates a first modified energy band profile 30 when a voltage isprovided in a reverse direction to MIM device 10. The voltage may beprovided by, for example, an applied external voltage or an inducedvoltage due to the incidence of electromagnetic energy. In this case,tunneling of the electrons (not shown) can occur in a reverse direction,represented by an arrow 36. In contrast, as shown in FIG. 1D, when avoltage is provided in a forward direction to MIM device 10, a secondmodified energy band profile 40 results. In the case of the situationshown in FIG. 1D, tunneling of the electrons can again occur but in aforward direction, represented by an arrow 46. FIG. 1E illustrates atypical I-V curve 50 of current (y-axis 52) as a function of voltage(x-axis 54) for MIM device 10. I-V curve 50 demonstrates that the MIMdevice functions as a rectifying element. An MIM device providesrectification and energy detection/conversion by tunneling of electronsbetween first and second metal layers 12 and 14.

[0008] Continuing to refer to FIGS. 1A-1E, in energy conversionapplications, it is further desirable to achieve high degrees ofasymmetry and nonlinearity and sufficiently high current magnitudes inthe current-to-voltage performance (I-V curve). If the current magnitudeis too low, the incident electromagnetic energy will not be collectedwith high efficiency. The required current magnitude is a function ofthe MIM device geometry, dielectric properties of the oxide, and thesize and number of the incident electromagnetic energy quanta. A higherdegree of asymmetry in the I-V curve between positive values of V(forward bias voltage) and negative values of V (reverse bias voltage)about the operating point results in better rectification performance ofthe device. In addition, the differential resistance of the device,which influences the responsivity and coupling efficiency of the deviceto incoming electromagnetic energy, is directly related to thenonlinearity of the I-V curve. An optimal value of differentialresistance is required to impedance match the MIM device to the antennaresulting in maximum power transfer to the device. The differentialresistance of MIM devices are often too large for energy conversionapplications and, consequently, it is desirable to lower differentialresistance values in order to impedance match the antenna. In otherwords, in solar energy conversion applications, it is preferable to havea higher degree of nonlinearity in the I-V curve and optimal value ofdifferential resistance in the device, thus yielding higher sensitivityof the device to incoming solar energy. As a result, high degrees ofasymmetry and nonlinearity in the current-to-voltage characteristics ofthe device yields high efficiency in the energy conversion process.Currently available MIM devices are not able to provide sufficientlyhigh degrees of asymmetry and nonlinearity with sufficiently lowdifferential resistance in the current-to-voltage performance, hence theenergy conversion efficiency of MIM devices is low.

[0009] A known alternative to the simple MIM device is a device withadditional metal and insulator layers, as demonstrated by Suemasu, etal. (Suemasu)⁷ and Asada, et al. (Asada).⁸ The devices of Suemasu andAsada have the configuration of MIMIMIM, in which the three insulatorlayers between the outer metal layers act as a triple-barrier structure.The insulator layers are crystalline insulator layers formed by anepitaxial growth procedure detailed in Ref. 7. The presence of thebarriers between the outer metal layers result in resonant tunneling ofthe electrons between the outer metal layers under the appropriate biasvoltage conditions, as opposed to simple, tunneling of the MIM device.The resonant tunneling mechanism in the electron transport yieldsincreased asymmetry and nonlinearity and reduced differential resistancevalues for the MIMIMIM device. The resonance tunneling also results in acharacteristic resonance peak in the current-voltage curve of thedevice, which yields a region of negative differential resistance andleads to the possibility of optical devices with very fast responses andhigh efficiency.

[0010] However, the MIMIMIM devices of Suemasu and Asada have thedistinct disadvantage of being a much more complicated device than thesimple MIM device. The fabrication procedure of Suemasu includes thedeposition of cobalt, silicon and calcium fluoride to form alternatinglayers of CoSi₂ and CaF₂. These rather exotic layer materials werechosen due to the crystalline lattice matching constraints inherent inthe epitaxial growth procedure. Several of the difficulties in thefabrication procedure, such as the problem with agglomeration of cobalton the CaF2 layer as well as the multiple photolithography and selectiveetching steps required to form the final device after the MIMIMIM layershave been grown, are described in Ref. 7. Suemasu also contends that theuse of a triple-barrier structure, rather than a slightly simplerdouble-barrier structure, is necessary in order to achieve negativedifferential resistance resulting from resonant tunneling using onlymetal and insulator layer combinations, thus avoiding the use ofsemiconductor materials. In addition, Suemasu requires that thethickness of the individual metal and insulator layers must be strictlycontrolled to the atomic layer level in order to achieve the resonancetunneling effect. Therefore, although the goal of increased nonlinearityand asymmetry may be achieved in the MIMIMIM devices of Suemasu andAsada using metal and insulator combinations, the simplicity of the MIMstructure is lost.

[0011] An alternative device structure that has been suggested toachieve resonant tunneling in semiconductor devices is the use of twoadjacent insulator layers between two semiconductor layers, resulting ina semiconductor-insulator-insulator-semiconductor (SIIS) structuredescribed by Papp, et al. (Papp).⁹ Papp describes a theoretical SIISstructure, in which the two crystalline insulator layers are formed oftwo different insulator materials by crystal growth techniques. The SIISstructure is said to yield a resonant tunneling effect with negativedifferential resistance, increased nonlinearity and asymmetry as well asnegative differential resistance, similar to that shown in theaforedescribed MIMIMIM devices of Suemasu and Asada, although an actualSIIS structure has not yet been implemented, to the Applicants'knowledge. Current crystal growth techniques theoretically enable theimplementation of the SIIS structure, but an SIIS device would stillembody the drawbacks inherent in semiconductor materials, namely costefficiency in large area devices. In addition, Suemasu (see Ref. 7)speculates that the recent trend of decreasing the size of electronicdevices in order to achieve high speed switching will makesemiconductor-based devices impractical due to fluctuation of carrierconcentration, which occurs when semiconductor devices are reduced tomesoscopic regimes.

[0012] The energy which is detected and converted by the MIM diode canbe delivered to the diode by means of an antenna as described by Fumeauxet. al. in [6]. The antennas used at infrared frequencies are typicallyplanar since they are fabricated using semiconductor fabricationtechniques such as metal evaporation and patterning. The bowtie antenna,in particular, is a popularly used antenna for infrared detectors sinceit is broadband and less susceptible to fabrication tolerances than adipole antenna. The detected signal is extracted from the diode by usinglow frequency leads. In previous work, low frequency leads have beenconnected across the bowtie antenna center terminals where the diode isconnected, or across the entirety of the outermost edges of the antennaarms. The former, which will be referred to as the center-fedarrangement is presented by Fumeaux et. al. [6]. The latter edge-fedarrangement is shown in one paper by Rutledge and Muha et. al. [10] aswell as in another paper by Rutledge et al. [11]. As will be describedat appropriate points below, the present invention recognizes certainproblems with both the center-fed arrangement and the edge-fedarrangement which are thought to be unresolved by the prior art.

[0013] As will be seen hereinafter, the present invention provides asignificant improvement over the prior art as discussed above by virtueof its ability to provide the increased performance while, at the sametime, having significant advantages in its manufacturability. Thisassertion is true for electromagnetic devices generally, which takeadvantage of the present invention, as well as solar energy conversiondevices in particular. Moreover, certain problems relating to prior artcenter-fed and edge-fed configurations are thought to be resolved.

REFERENCES

[0014] 1. J. G. Simmons, “Electric tunnel effect between dissimilarelectrodes separated by a thin insulating film,” Journal of AppliedPhysics, 34 (1963).

[0015] 2. S. R. Pollack and C. E. Morris, “Electron tunneling throughasymmetric films of thermally grown Al₂O₃ ,” Journal of Applied Physics,vol. 35, no. 5 (1964).

[0016] 3. L. O. Hocker, et al., “Frequency mixing in the infrared andfar-infrared using a metal-to-metal point contact diode,” AppliedPhysics Letters, vol. 12, no. 12 (1968).

[0017] 4. S. M. Faris, et al., “Detection of optical and infraredradiation with DC-biased electron-tunneling metal-barrier-metal diodes,”IEEE Journal of Quantum Electronics, vol. QE-9, no. 7 (1973).

[0018] 5. B. Michael Kale, “Electron tunneling devices in optics,”Optical Engineering, vol. 24, no. 2 (1985).

[0019] 6. C. Fumeaux, et al., “Nanometer thin-film Ni—NiO—Ni diodes fordetection and mixing of 30 THz radiation,” Infrared Physics andTechnology, 39 (1998).

[0020] 7. T. Suemasu, et al., “Metal (CoSi₂)/Insulator(CaF₂) resonanttunneling diode,” Japanese Journal of Applied Physics, vol. 33 (1994).

[0021] 8. M. Asada, et al., “Theoretical analysis and fabrication ofsmall area Metal/Insulator resonant tunneling diode integrated withpatch antenna for terahertz photon assisted tunneling,” Solid StateElectronics, vol. 42, no. 7-8 (1998).

[0022] 9. G. Papp, et al., “Current rectification through asingle-barrier resonant tunneling quantum structure,” Superlattices andMicrostructures, vol. 17, no. 3 (1995).

[0023] 10. Rutledge, D. B., and Muha, M. S., “Imaging Antenna Arrays,”IEEE Trans. On Antennas and Propagation, Vol. AP-30, 1982, pp. 535-540.

[0024] 11. Rutledge, D. B., Neikirk, D. P., and Kasilingam, D. P.,Chapter 1, page 25, “Infrared and Millimeter Waves,” Vol. 10, Edited byKenneth J. Button.

SUMMARY OF THE INVENTION

[0025] As will be described in more detail hereinafter, there isdisclosed herein an electron tunneling device including first and secondnon-insulating layers. The first and second non-insulating layers arespaced apart from one another such that a given voltage can be providedacross the first and second non-insulating layers, either by an appliedexternal bias voltage or, for example by an induced voltage due to theincidence of solar energy without an applied voltage or both. Theelectron tunneling device further includes an arrangement disposedbetween the first and second non-insulating layers and configured toserve as a transport of electrons between the first and secondnon-insulating layers. This arrangement includes a first layer of anamorphous material configured such that using only the first layer ofthe amorphous material in the arrangement would result in a given valueof a first parameter in the transport of electrons, with respect to thegiven voltage. However, in accordance with one aspect of the invention,the arrangement includes a second layer of material, which second layeris configured to cooperate with the first layer of amorphous materialsuch that the transport of electrons includes, at least in part,transport by a mechanism of tunneling, and such that the firstparameter, with respect to the given voltage, is increased over andabove the given value of the first parameter. The first parameter is,for example, nonlinearity or asymmetry in the electron transport.

[0026] In another aspect of the invention, the first layer of amorphousmaterial, if used alone in the arrangement of the electron tunnelingdevice, would result in a given value of a second parameter in thetransport of electrons, with respect to the given voltage, but thesecond layer of material is also configured to cooperate with the firstlayer of amorphous material such that second parameter in the transportof electrons, with respect to the given voltage, is reduced below thegiven value of the second parameter. The second parameter is, forexample, differential resistance.

[0027] In yet another aspect of the invention, a device for convertingsolar energy incident thereon into electrical energy is described. Thedevice has an output and provides the electrical energy at the output.The device includes first and second non-insulating layers spaced apartfrom one another such that a given voltage can be provided across thefirst and second non-insulating layers. The device also includes anarrangement disposed between the first and second non-insulating layersand configured to serve as a transport of electrons between the firstand second non-insulating layers. The arrangement includes a first layerof an amorphous material. The arrangement also includes a second layerof material configured to cooperate with the first layer of theamorphous material such that the transport of electrons includes, atleast in part, transport by a mechanism of tunneling, and such that thesolar energy incident on the first and second non-insulating layers, atleast in part, is extractable as electrical energy at the output.

[0028] In a further aspect of the present invention, an assemblyincludes a device configured for receiving at least one input to producean output responsive thereto. An antenna arrangement supports the deviceto transfer the input to the device and further to transfer the outputfrom the device such that the antenna arrangement supports a selectedone of the input and the output as a high frequency current and theantenna arrangement includes a peripheral configuration which confinesthe high frequency current to at least one dominant path within theantenna arrangement so that the high frequency current oscillates in thedominant path and so that the other one of the input and the output is alower frequency signal that is present at least generally throughout theantenna arrangement. At least one port, within the antenna arrangement,is positioned sufficiently away from the dominant path so as to isolatethe lower frequency signal at the port from the high frequency currentin the dominant path.

[0029] In a continuing aspect of the present invention, an assemblyincludes a device configured for receiving at least one input to producean output responsive thereto. An antenna arrangement supports the deviceto transfer the input to the device and further to transfer the outputfrom the device such that the antenna arrangement supports a selectedone of the input and the output as a high frequency current and theantenna arrangement includes a peripheral configuration which confinesthe high frequency current to at least one dominant path within theantenna arrangement and the other one of the input and the output is alower frequency signal that is present at least generally throughout theantenna arrangement. At least one port, within the antenna arrangement,at a location selected such that the high frequency current travels pastthe port in at least one direction that is away from the device, and theport is positioned sufficiently away from the dominant path so as toisolate the lower frequency signal at the port from the high frequencycurrent in the dominant path.

[0030] In an additional aspect of the present invention, an assemblyincludes a device configured for receiving at least one input to producean output responsive thereto. An antenna arrangement supports the deviceto transfer the input to the device and further to transfer the outputfrom the device such that the antenna arrangement supports a selectedone of the input and the output as a high frequency current and theantenna arrangement includes a peripheral configuration which confinesthe high frequency current to at least one resonant path within theantenna arrangement so that the high frequency current oscillates in theresonant path between a pair of opposing first and second reflectorconfigurations that are formed as part of the peripheral outline and sothat the other one of the input and the output is a lower frequencysignal that is present at least generally throughout the antennaarrangement. At least one port, within the antenna arrangement, whichport is positioned sufficiently away from each one of the first andsecond reflector configurations so as to sustain reflection of thesurface current in the resonant path while conducting the lowerfrequency signal.

[0031] In another aspect of the present invention, an assembly includesa device configured for receiving at least one input to produce anoutput responsive thereto. An antenna arrangement includes a bowtieperipheral configuration defining a bowtie intersection for supportingthe device at the bowtie intersection to transfer the input to thedevice and further to transfer the output from the device such that theantenna arrangement supports a selected one of the input and the outputas a high frequency current and the bowtie peripheral configurationconfines the high frequency current to at least one dominant path withinthe antenna arrangement so that the high frequency current oscillates inthe dominant path traveling through the bowtie intersection and so thatthe other one of the input and the output is a lower frequency signalthat is present at least generally throughout the antenna arrangement.At least one port, within the antenna arrangement, is positioned spacedapart from the bowtie intersection and sufficiently away from thedominant path or paths so as to isolate the lower frequency signal atthe port from the high frequency current in the dominant path.

[0032] In a related feature, an assembly produced in accordance with thepresent invention may be configured for operation in any one of amodulation mode, a mixing mode, a detection mode and an emitting modedependent upon the type of active device that forms part of theassembly.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention may be understood by reference to thefollowing detailed description taken in conjunction with the drawingsbriefly described below.

[0034]FIG. 1A is a diagrammatic illustration of a prior art device usinga metal-insulator-metal (MIM) configuration.

[0035]FIGS. 1B-1D are graphs illustrating the schematic energy bandprofiles of the MIM device of FIG. 1A for various voltages providedacross the MIM device.

[0036]FIG. 1E is a graph of a typical current-voltage curve for the MIMdevice of FIG. 1A.

[0037]FIG. 2A is a diagrammatic illustration of an electron tunnelingdevice designed in accordance with the present invention.

[0038]FIG. 2B-2D are graphs illustrating the schematic energy bandprofiles of the electron tunneling device of FIG. 2A for variousvoltages provided across the electron tunneling device.

[0039]FIG. 2E is a graph of a typical current-voltage curve for theelectron tunneling device of FIG. 2A.

[0040]FIG. 3A is a diagrammatic top view of a device for convertingsolar energy incident thereon into electrical energy, designed inaccordance with the present invention, shown here to illustrate apossible configuration of metal layers of the device.

[0041]FIG. 3B is a cross sectional view of the device of FIG. 3A, shownhere to illustrate additional structure positioned between the metallayers of the device.

[0042]FIG. 4 is a diagrammatic illustration of an electron tunnelingdevice of the present invention including a superlattice structure.

[0043]FIG. 5 is a diagrammatic illustration, in plan view, of a deviceintegrated antenna assembly of the present invention, shown here toillustrate a resonant bowtie configuration having outermost endsincluding cooperating reflection segments and outset ports.

[0044]FIG. 6A is a diagrammatic illustration, in plan view, of a deviceintegrated antenna assembly of the present invention, shown here toillustrate a resonant bowtie configuration having outermost endsincluding cooperating reflection segments and inset ports.

[0045]FIG. 6B is a diagrammatic illustration, in plan view, of one ofthe bow arms of the antenna of FIG. 6A, shown here to illustrate detailswith regard to design considerations in relation to the dominant pathsdefined by the antenna.

[0046]FIG. 7 is a diagrammatic illustration, in plan view, of a deviceintegrated antenna assembly of the present invention, shown here toillustrate a non-resonant bowtie configuration having outermost endsincluding cooperating reflection segments and inset ports.

DETAILED DESCRIPTION

[0047] The following description is presented to enable one of ordinaryskill in the art to make and use the invention and is provided in thecontext of a patent application and its requirements. Variousmodifications to the described embodiments will be readily apparent tothose skilled in the art and the generic principles herein may beapplied to other embodiments. Thus, the present invention is notintended to be limited to the embodiment shown but is to be accorded thewidest scope consistent with the principles and features describedherein.

[0048] Referring now to FIG. 2A, an electron tunneling device designedin accordance with the present invention is described. The electrontunneling device, generally indicated by reference number 110, includesa first non-insulating layer 112 and a second non-insulating layer 114.Non-insulating materials include, for example, metals, superconductors,semiconductors, semimetals, quantum wells and superlattice structures.First non-insulating layer 112 and second non-insulating layer 114 canbe formed, for example, of two different metals, such as chromium andaluminum, by conventional methods such as, but not limited to, thermalevaporation and sputtering. First non-insulating layer 112 and secondnon-insulating layer 114 are spaced apart such that a given voltage canbe provided therebetween. The given voltage can be, for instance, a biasvoltage from an external voltage source (not shown) that is directlyapplied to the first and second non-insulating layers. Alternatively, aswill be seen, the given voltage can be induced by, for example, solarenergy. Furthermore, the given voltage can be a combination of inducedvoltage (from incident electromagnetic radiation, for example) and anapplied external bias voltage.

[0049] Continuing to refer to FIG. 2A, a first amorphous layer 116 isdisposed between first non-insulating layer 112 and secondnon-insulating layer 114. For purposes of this application, an amorphousmaterial is considered to include all materials which are not singlecrystal in structure. First amorphous layer 116 can be, for example, anative oxide of first non-insulating layer 112. For instance, if a layerof chromium is used as first non-insulating layer 112, the layer ofchromium can be oxidized to form a layer of chromium oxide to serve asfirst amorphous layer 116. Other suitable materials include, but are notlimited to, silicon dioxide, niobium oxide, titanium oxide, aluminumoxide, zirconium oxide, tantalum oxide, hafnium oxide, yttrium oxide,magnesium oxide, silicon nitride and aluminum nitride. Electrontunneling device 110 further includes a second layer 118 positionedbetween first non-insulating layer 112 and second non-insulating layer114. Second layer 118 is formed of a predetermined material, which isdifferent from first amorphous layer 116 and is configured to cooperatewith first amorphous layer 116 such that first amorphous layer andsecond layer 118 serve as a transport of electrons between the first andsecond non-insulating layers. The predetermined material, which formssecond layer 118, can be, for example, an amorphous insulator such as,but not limited to, chromium oxide, silicon dioxide, niobium oxide,titanium oxide, aluminum oxide, zirconium oxide, tantalum oxide, hafniumoxide, yttrium oxide, magnesium oxide, silicon nitride, aluminum nitrideand a simple air or vacuum gap. Preferably, second layer 118 is formedof a material having a lower or higher work function than that of firstamorphous layer such that the device exhibits an asymmetry in the energyband diagram.

[0050] Had the device consisted of only the first and secondnon-insulating layers and the first amorphous layer, the device would beessentially equivalent to the prior art MIM device and would exhibit agiven degree of nonlinearity, asymmetry and differential resistance inthe transport of electrons. However, the inclusion of second layer 118,surprising and unexpectedly, results in increased degrees ofnonlinearity and asymmetry over and above the given degree ofnonlinearity and asymmetry while the differential resistance is reduced,with respect to the given voltage. This increase in the nonlinearity andasymmetry and reduction in differential resistance is achieved withoutresorting to the use of epitaxial growth techniques or crystallinelayers of the aforedescribed prior art. The mechanism of this increaseis described immediately hereinafter in reference to FIGS. 2B-2E.

[0051] Referring to FIG. 2B in conjunction with FIGS. 1B and 2A, aschematic of a energy band profile 120 corresponding to electrontunneling device 110 is illustrated. Energy band profile 120 includesfour regions corresponding to the four layers of electron tunnelingdevice 110, in comparison to the three regions shown in energy bandprofile 20 of the prior art MIM device. The presence of second layer 118contributes to the change in the energy band profile of electrontunneling device 110.

[0052] Turning now to FIGS. 2C and 2D in conjunction with FIGS. 1C and1D, the changes in the energy band profile due to voltage applicationare shown. During reverse bias operation of electron tunneling device110, the energy band profile changes to that shown as line 130, which isrelatively similar to the case of reverse bias operation shown in FIG.1C for the MIM device. In the situation shown in FIG. 2C, the primarymechanism by which electrons travel between the first and secondnon-insulating layers is tunneling in a reverse direction indicated byan arrow 136. When a forward bias voltage is provided, however, amodified energy band profile 140 of FIG. 2D results. In this case,tunneling occurs in paths 146 and 146′, but there now exists a quantumwell region through which resonant tunneling occurs, as shown by arrow148. In the region of resonant tunneling, the ease of transport ofelectrons suddenly increase, therefore resulting in increased currentbetween the non-insulating layers of electron tunneling device 110.

[0053] Continuing to refer to FIG. 2D, the addition of second layer 118provides a path for electrons to travel through the device by a resonanttunneling rather than the tunneling process of the prior art MIM device.As a result, more current flows between the non-insulating layers ofelectron tunneling device 110, as compared to the MIM device, when apositive voltage is provided while the current flow with a negativevoltage provided to the electron tunneling device of the presentinvention. The presence of resonant tunneling in electron tunnelingdevice 110 therefore results in increased nonlinearity and asymmetry incomparison to the prior art MIM device.

[0054] A typical I-V curve 150 corresponding to electron tunnelingdevice 110 is shown in FIG. 2E. I-V curve 150 demonstrates that electrontunneling device 110 functions as a diode, where the diode is defined asa two-terminal electronic element. Furthermore, I-V curve 150 is shownto include a resonance peak 156 corresponding to the provided voltageregion in which resonant tunneling occurs. The appearance of resonanttunneling in actually fabricated devices of the present inventiondepends on the precision of the fabrication process. Even when resonancepeak 156 is not present, I-V curve 150 exhibits a higher degree ofasymmetry and nonlinearity in comparison to the I-V curve of the priorart MIM device (as shown in FIG. 1E). In other words, while the presenceof a resonance peak in the I-V curve of an electron tunneling device ofthe present invention may lead to additional advantages in certainapplications, such as greatly increased nonlinearity around theresonance peak, the electron tunneling device of the present inventionachieves the goal of increased asymmetry and nonlinearity with reduceddifferential resistance in the current-to-voltage performance even whenthe averaging effect of the amorphous layer “washes out” the resonancepeak. Therefore, electron tunneling device 110 essentially includes allof the advantages of the prior art MIMIMIM device, without thecomplicated fabrication procedure and the use of exotic materials, andall of the advantages of the prior art SIIS device, without thedrawbacks of the use of semiconductor materials as described above.Despite and contrary to the teachings of Suemasu, the electron tunnelingdevice of the present invention is able to achieve increasednonlinearity and asymmetry and decreased differential resistance in thetransport of electrons through the device, using readily availablemetals and insulators in a simple structure that is simply manufacturedcompared to the more complex manufacturing processes of the prior art.

[0055] It is emphasized that the electron tunneling device of thepresent invention combines the simplicity of the MIM device with theperformance characteristics of the MIMIMIM devices of Suemasu and Asadawhile using readily available materials and avoiding the use ofsemiconductors. Although superficially similar to the SIIS device instructure at first glance due to the presence of two adjacent insulatorlayers, the addition of second layer 118 in electron tunneling device110 is not easily accomplished due to fundamental differences in thefabrication procedure (crystal growth and doping techniques in thesemiconductor devices versus the oxidation and deposition techniquesused in the present invention). In fact, Suemasu and Asada resort to themore complex MIMIMIM structure formed by epitaxial growth techniques inorder to achieve the same resonant tunneling effect. The crystallinegrowth and epitaxial growth techniques used in the SIIS device of Pappand the MIMIMIM devices of Suemasu and Asada preclude the use ofamorphous insulator materials in the SIIS device or the MIMIMIM devicesince crystalline growth and epitaxial growth techniques, by definition,are able to form only crystalline layers. In fact, the crystallinematerials that may be used in the SIIS device or the MIMIMIM device arelimited by substrate compatibility (for the SIIS device) and crystallinelattice matching considerations (in the MIMIMIM device); that is, thespecific materials that may be used in the devices of Suemasu, Asada andPapp are limited by the fabrication procedures used in manufacturingthese devices.

[0056] In contrast, the insulator materials used in the electrontunneling device of the present invention may be chosen from a varietyof oxides and other materials that can be deposited by sputtering,atomic layer deposition, spin-on deposition, and other readily availabletechniques. For example, a thin layer of metal can be deposited thenoxidized to form the insulator layer. Layer adhesion may be promoted bya surfactant such as one containing silanes or organic materials. Inother words, the specific choice of materials used in the electrontunneling device of the present invention can be chosen for the desiredelectronic characteristics of the materials, rather than being limitedin the choice by the fabrication procedure. Furthermore, the inclusionof the amorphous insulator in combination with the second layer ofmaterial in the electron tunneling device of the present inventionyields unexpected advantages, such as resonant tunneling. The simplicityof the electron tunneling device of the present invention yieldsadvantages not available in the SIIS nor the MIMIMIM device in the easeof fabrication and the flexibility in the selection of materials.Moreover, the use of an amorphous insulator layer in the device, whichis not feasible in the MIMIMIM devices of Suemasu and Asada nor the SIISdevice of Papp due to the epitaxial growth technique requirements,allows added flexibility in the selection of materials in the presentdevice, since amorphous rather than only compatible crystalline layerscan be used, thus further distinguishing the electron tunneling deviceof the present invention from the prior art devices.

[0057] The resonant tunneling effect and increased asymmetry andnonlinearity and reduced differential resistance in the electrontunneling device of the present invention have been verified by theApplicants by theory and experiment. In theoretical calculations, thecurrently available models for MIM devices were extensively modified inaccordance with re-analysis of fundamental algorithms and evaluation toallow the modeling of the electron tunneling device of the presentinvention. The results of the theoretical calculations verified thepresence of resonant tunneling and increased asymmetry and nonlinearitywith reduced differential resistance in the electron tunneling device ofthe configuration shown in FIG. 2A.

[0058] Experimental devices were also fabricated in accordance with thepresent invention and tested. A thin film deposition method based onatomic layer deposition (ALD) techniques was used in the fabrication ofthe second layer. Other deposition techniques, such as but not limitedto sputtering may also be used in place of ALD. The fabrication processdescribed below utilizes a lift-off technique to form the patternedmetal layers. Formation of the patterned metal layer is also possible bychemical etching, reactive ion etching, milling and other techniques. Asummary of the fabrication process for a typical device is as follows:

[0059] 1. Thoroughly clean a silicon wafer substrate including a thermaloxide less than 1 μm thick for electrical isolation between the MIMdiode and silicon substrate using a combination of baking steps andde-ionized (DI) water rinses;

[0060] 2. Form a base contact pad, which is resistant to the formationof a continuous ALD insulator, to function as an antenna and contactpads (for electrically accessing the device):

[0061] a. Lithography to define the contact pad shape:

[0062] i. O₂ plasma cleaning to de-scum the silicon wafer,

[0063] ii. Spin on a primer (HMDS) at 6000 rpm for 30 seconds,

[0064] iii. Spin on a resist at 6000 rpm for 30 seconds (time and spinspeed are dependent on the specific resist used),

[0065] iv. Pre-bake the resist layer at 90° C. for 25 minutes (time andtemperature are dependent on the specific resist used),

[0066] v. Expose the resist layer for 27 seconds (exposure time isdependent on the specific resist used and the resist thickness),

[0067] vi. Develop the resist layer using a developer solution (4:1ratio of DI water to developer) for a predetermined time, (developersolution depends upon specific resist and developer used)

[0068] vii. Rinse off the developer with DI water,

[0069] viii. 02 plasma cleaning to clean the resist openings;

[0070] b. Thermal evaporation of bond layer (100 nm of chromium) toserve as a scratch-resistant metal, through which the device can beelectrically probed;

[0071] c. Thermal evaporation of contact layer (100 nm of gold) forpreventing the oxidation of the bond layer and the adhesion of acontinuous ALD layer;

[0072] d. Lift-off to remove extraneous material:

[0073] i. Lift-off with acetone on spinner at low speed,

[0074] ii. Ultrasonic bath with acetone (if necessary to promotelift-off),

[0075] iii. Lift-off with acetone on spinner,

[0076] iv. Clean with isopropyl alcohol on spinner,

[0077] v. Spin dry;

[0078] 3. Form a first non-insulating layer by repeating Step 2 (skipStep 2c) to form a 100 nm-thick Cr layer;

[0079] 4. Form a first amorphous layer by oxidizing (3 days minimumunder a clean hood) the first non-insulating layer to form a nativeoxide, less than 4 nm in thickness;

[0080] 5. Form a second layer by atomic layer deposition using Al(CH₃)₃and H₂O precursors;

[0081] 6. Form the second non-insulating layer by repeating Step 3.

[0082] The fabrication procedure described above is relatively simple,compared to the fabrication procedure of the MIMIMIM devices of Suemasuand Asada described above, and is flexible, allowing the use of variousmetal and oxide materials. As mentioned above, a variety of metals, suchas but not limited to chromium, aluminum, niobium, tungsten, nickel,yttrium and magnesium, and a variety of oxides, such as the nativeoxides of the aforementioned various metals or other oxides that can bedeposited onto existing amorphous layers are suitable for use in theelectron tunneling device of the present invention. The resultingdevices have been measured to verify the presence of the resonance peakin the I-V curve as well as the increased asymmetry and nonlinearitywith reduced differential resistance. Attention is particularly directedto Step 2c, in which an additional contact layer of a metal, such assilver or gold, is deposited on top of the chromium bond layer. In thisway, the contact pad is still accessible while the insulators depositedby atomic layer deposition do not form a continuous layer. In addition,other methods of lithography, such as electron beam-assistedlithography, may be used in place of the aforedescribed photolithographysteps. Also, in step 1, the coupling between the antenna andelectromagnetic energy may altered by alternative substrate choices suchas, but not limited to, glass, quartz and other non-conductive materialsthat are flat and capable of withstanding the evaporation and depositionprocedures, such as those described above. Furthermore, if coupling ofthe electromagnetic radiation from the substrate side of the device isdesired a substrate transparent to the incident electromagneticradiation can be used in place of the silicon wafer substrate.

[0083] Turning now to FIGS. 3A and 3B, a solar energy converter 200 hasbeen developed as one application example of the present invention asdescribed above. Solar energy converter 200 includes a firstnon-insulating layer 212 and a second non-insulating layer 214corresponding to previously described layers 112 and 114, respectively.An overlap portion between the first and second non-insulating layers,indicated by a box 215, effectively forms the aforedescribed electrontunneling device. The structure of the electron tunneling device isshown more clearly in FIG. 3B, illustrating a cross sectional view ofsolar energy converter 200 of FIG. 3A taken along line 3B-3B. A firstamorphous insulator layer 216 and a second layer 218, corresponding topreviously described layers 116 and 118, respectively, are positioned inoverlap portion 215 of the first and second non-insulating layers toresult in the electron tunneling device of the present invention.

[0084] As shown in FIG. 3A, first and second non-insulating layers 212and 214, respectively, are further shaped in a form of a bow-tie antennato focus the incident solar energy on the overlap portion, thusincreasing the sensitivity of the solar energy converter to incidentsolar energy. The bow-tie antenna is configured to increase thesensitivity of solar energy converter 200 to broadband solar energy bybeing receptive to electromagnetic radiation over a range offrequencies, for example, from near-ultraviolet to near-infraredfrequencies. When solar energy 220 falls on solar energy converter 200,solar energy 220 is converted to a voltage between the first and secondnon-insulating layers to serve as the aforementioned given voltage. Adirectional current is established in the overlap portion in accordancewith the I-V curve for the electron tunneling device of the presentinvention. Thus, the incident solar energy is converted to electricalenergy by electrical rectification. The electrical energy can then beextracted at an output from the solar energy converter.

[0085] It is stressed that the solar energy converter of FIGS. 3A and 3Bexhibit the performance advantages of the MIMIMIM and SIIS devices whileavoiding the disadvantages of the prior art devices. Namely, solarenergy converter 200 is based on a simple structure of twonon-insulating layers separated by two different layers positionedtherebetween, where one of the two different layers is an amorphousinsulator. Due to the flexible fabrication process, the exact materialsused in solar energy converter 200 can be selected from a wide varietyof readily available materials, such as chromium, aluminum, titanium,niobium and silicon and the respective native oxides, and not beconstrained to the use of only semiconductor materials, crystallineinsulators or exotic materials, such as CoSi₂. Also, unlike the priorart semiconductor device, which is limited in its response by thebandgap energy, the solar energy converter of the present invention issensitive to a wide range of incident electromagnetic energies. In fact,with an appropriately designed antenna, which is configured to besensitive to the range of frequencies within the electromagneticspectrum of the sun, the energy conversion efficiency upper limit of thesolar energy converter of the present invention approaches 100% of theenergy delivered to the electron tunneling device by the antenna.Moreover, the solar energy converter of FIGS. 3A and 3B does not requirethe application of an external bias voltage, other than the solar energyreceived by the antenna structure. The fact that the solar energyconverter of the present invention does not require the application ofan external bias is in contrast to prior art devices which require theapplication of an external bias voltage.

[0086] Turning now to FIG. 4, a variation of the electron tunnelingdevice of the present invention is described. FIG. 4 illustrates anelectron tunneling device 300 including a superlattice structure 310positioned between first non-insulating layer 12 and secondnon-insulating layer 14. Superlattice structure 310 includes a pluralityof thin non-insulating layers 312 separated by thin insulating layers314. Each thin non-insulating layer 312 can be, for example, onemonolayer of a metal, and each thin insulating layer 314 can be, forinstance, seven monolayers of an insulator. Superlattice structure 310provides an transport path for electrons, thus increasing electron flowbetween the first and second non-insulating layers. As a result, moreflexibility in the design of the electron tunneling device becomesavailable for enhancing the performance of the device such as, forinstance, increasing the device nonlinearity by selecting a suitablematerial to modify the height of the energy band corresponding to eitherthe first or the second non-insulating layer.

[0087] Although each of the aforedescribed embodiments have beenillustrated with various components having particular respectiveorientations, it should be understood that the present invention maytake on a variety of specific configurations with the various componentsbeing located in a wide variety of positions and mutual orientations andstill remain within the spirit and scope of the present invention.Furthermore, suitable equivalents may be used in place of or in additionto the various components, the function and use of such substitute oradditional components being held to be familiar to those skilled in theart and are therefore regarded as falling within the scope of thepresent invention. For example, the exact materials used in theaforedescribed devices may be modified while achieving the same resultof improved current-voltage performance. Also, in the solar energyconverter application, other antenna shapes suitable for receivingbroadband solar energy may be used in place of the bow-tie antenna.

[0088] In addition to the advantages described thus far resulting fromresonant tunneling, asymmetry may be further enhanced by quantummechanical reflections. Quantum mechanical reflections occur as a resultof changes in potential energy or effective mass and are accounted forin the inventors' theoretical calculations. These reflections result forelectrons tunneling both above and below the band edge of the insulator.As a result of the substantially different barrier and effective massprofile of this multilayer system over single layer MIM diodes asymmetrywill be enhanced even in the absence of the resonant tunneling.

[0089] Furthermore, it is noted that the slope of the conduction band inthe oxide is proportional to the electric field strength, and theelectric field strength in turn depends upon the dielectric constantwithin the oxide. Consequently, we may tailor the voltage drop orelectric field strength across each of the oxide regions by using oxideswith desirable dielectric constants. By controlling the electric fieldstrength in each layer we may further tailor the resonant energy levelslocation as a function of provided voltage.

[0090] Moreover, the asymmetry in the I-V curve of the device can befurther enhanced by considering the electric field direction in themultilayer system. In tunneling, the electric field direction does notplay a role in the magnitude of the tunneling probability. However, ifan electron does not tunnel the entire distance through the oxide,perhaps due to a collision, the characteristics of the electric fieldwill influence the post-collision electron direction. The direction,magnitude, and distribution of the electric field in the oxide layer canbe controlled by selecting the work functions and Fermi levels of theelectrodes and the dielectric constant of the oxide layers.

[0091] Referring briefly to FIG. 3A, it should be noted that outputs aretaken from opposing outermost ends of first and second non-insulatinglayers 212 and 214. A still more detailed discussion of this highlyadvantageous configuration follows immediately hereinafter. Moreover, itshould be noted that even though solar energy conversion has beendiscussed above, the present invention enjoys a broad range ofapplicability including high-speed detection, heterodyne mixing andmodulation of optical communication signals, emission of opticalradiation, millimeter wave and sub-millimeter wave detection for thermalimaging, as well as emission of electromagnetic energy. In addition, thedevice integrated with the antenna can take on forms other than the MIMor MIIM diodes discussed here. For example, devices which arecontemplated as being useful include, but are not limited to diode typessuch as MIM, MIIM, SIS and Schottky, and devices such as microbolometersand Josephson junctions. The application will primarily be determined bythe capabilities of the device integrated with the antenna. For ahigh-speed diode as the device, communication applications may beattractive, whereas for a slower speed microbolometer, a thermal imagingapplication might be more suitable. For the highest sensitivity, aJosephson junction as the device might be more useful.

[0092] As indicated by the foregoing list of applications, the deviceintegrated antenna presented here can be used as a detector, amodulator, a mixer or an emitter of electromagnetic radiation. Thesemodes of operation will be briefly described below. The inputs andoutputs of the invention are either electrical or optical signals. Anelectrical signal is an electromagnetic signal traveling on electricalwires, whereas an optical signal is one that travels in a dielectricmedium such as a waveguide or free space.

[0093] A detector captures and converts an optical signal into anelectrical form. If the optical signal has been modulated, then thedetector will extract the modulating signal in electrical form. Themodulating signal is slowly varying in time in comparison with thehigher frequency of the received electromagnetic radiation. A mixer canbe thought of as a special case of a detector where two electromagneticsignals of different frequencies are received. These two frequencies arethen mixed and converted into a lower frequency which is extracted as anelectrical signal from the mixer.

[0094] As a modulator, the present invention will captureelectromagnetic radiation, imprint a modulating electrical signal uponit, and reradiate the final modulated signal. The emitter configurationis a special case of the modulator where an input electrical signalcauses the emission of an electromagnetic signal in optical form.

[0095] In order to describe the basic operation of the invention, it isdecomposed into three basic constituents as follows: an antenna, adevice, and low frequency leads. The function of the antenna is tocapture or radiate electromagnetic energy. The device integrated withthe antenna has the ability to detect, modulate, or emit electromagneticradiation. The low frequency leads are used to DC bias the device, ifnecessary, and also to carry the detected or modulating signal. Thebasic detector operation of the unit is that the antenna captureselectromagnetic energy from free space or a waveguide and couples itinto the device connected across the antenna terminals. This deviceconverts the electromagnetic energy into an electrical signal which istransferred away from the antenna-diode configuration by low frequencyleads. In modulator mode, the captured electromagnetic energy from theantenna is modulated by a varying electrical signal on the low frequencyleads.

[0096] Attention is now directed to FIG. 5 which diagrammaticallyillustrates a highly advantageous device integrated antenna assemblythat is generally indicated by the reference number 400. Assembly 400includes first and second non-insulating layers 212 and 214,respectively, each of which is in the form of a bow arm having outermostends 402 and 404 which are positioned farthest from a device (notvisible in this view) that is arranged proximate to the innermost endsof the bow arms between confronting portions thereof. This devicearrangement is essentially identical to that shown in cross-section inFIG. 3B and described above with certain exceptions to be noted.Initially, for example, it should be appreciated that the device used inFIG. 5 may be operable in any of the modes discussed above, where theantenna is integrated with any of the devices listed above.

[0097] Still referring to FIG. 5, for convenience in these descriptions,the bow arms may be referred to as such using reference numbers 212 and214. Accordingly, bow arms 212 and 214 cooperatively define a bowtieshaped peripheral outline 406. The bow arms further include first andsecond ports indicated by the reference numbers 408 and 410,respectively. In the present example, the ports are outset with respectto the outermost ends 402 and 404 of the bow arms, however, this is nota requirement, as is demonstrated by previously described FIG. 3A. Theelongated, outset ports may be formed, for example, as extensions ofnon-insulating layers 212 and 214, respectively. The ports merge into alow frequency transmission line that is diagrammatically indicated bythe reference number 412 leading to an input/output port 414. The portsmay merge into any suitable electrical transmission line such as, forexample, a coplanar stripline (CPS), which is not shown. In the CPS,signal propagation characteristics are determined primarily by the widthand spacing of the lines as well as the dielectric properties of thesubstrate which supports the lines. CPS design considerations aredescribed, as an example, by G. Ghione and C. Naldi in “Analyticalformulas for coplanar lines in hybrid and monolithic MIC's,” appearingin, Electron Letters, vol. 20, pages 179-181, 1984, which isincorporated by reference. During operational use, it should beunderstood that ports 408 and 410 may serve as either inputs or asoutputs depending upon whether the arrangement is operating in amodulation mode or in a detection mode, respectively. In both modulationor detection mode, if a DC bias is needed for the proper operation ofthe device, the ports 408 and 410 may serve as both a bias line as wellas an input or output line. In the instance where the arrangement isoperating in the modulation mode, ports 408 and 410 serve as inputswhereby to inject an input electrical signal at a given frequency. Thisgiven frequency may reside in a frequency range of approximately DC toseveral terahertz and is selected such that the wavelength at thisfrequency is significantly larger than the bowtie antenna in a way whichcauses the input electrical signal to be present at least generallythroughout the antenna arrangement. That is, a voltage induced acrossthe first and second non-insulating layers is not confined as tospecific regions of the bow arms. As a result, a modulation device atthe center of the bowtie configuration readily receives the inputelectrical signal. For bow arm 212, the input electrical signal is shownas a modulation mode input signal 420, indicated by an arrow, along apath extending from port 408 directly to the modulation device. It is tobe understood that such a modulation mode input signal also travels fromport 410 to the modulation device, but has not been shown due toillustrative constraints.

[0098] At the same time, an incident electromagnetic wave 421 such as,for example, ambient light is incident upon bow arms 212 and 214 so asto induce high frequency “surface” currents. While these currents may bereferred to in this description as well as in the appended claims usingthe terms high frequency currents or “surface currents”, it is to beunderstood that the current being described is present at or proximateto the surface of each bow arm and is additionally induced up to somedepth, from a practical standpoint, into the non-insulating body of thebow arm carrying the current. Generally, such surface current decaysrapidly with increasing depth into its conducting body so as to exhibitsignificantly higher magnitudes in the immediate vicinity of thesurface.

[0099] Still considering details with regard to the subject surfacecurrents, because the wavelength characterizing the surface currents isrelatively small in comparison to the geometry of the bowtie antenna,another important property of the surface currents arises. Specifically,and again unlike the input electrical signal, the surface currents arenot only confined depthwise in the bow arms, but are also confined in alateral sense on the surface of the bow arms at which they are induced.While, the low frequency electrical signal is uniformly present acrossthe lateral extents of the bow arms which make up the antennaarrangement, the surface currents are confined in the plane of FIG. 5,to particular paths within the antenna arrangement which are defined, atleast in part, by the peripheral outline or configuration of the bowtieantenna itself. These paths are referred to herein as dominant paths ormay be referred to, in the instance of a resonant antenna, as resonantpaths. In the case of a bowtie antenna, a pair of dominant paths ispresent. A first one of the dominant paths is shown as a first dashedline that is indicated by the reference number 430 and which is definedalong a first side margin of each of the bow arms. A second one of thedominant paths is shown as a second dashed line that is indicated by thereference number 432 and which is defined along an opposing, second sidemargin of each of the bow arms. Each of the dominant paths passesthrough or intersects the device that is positioned between theconfronting portions of the bow arms at their innermost ends. Themodulation device responds to the input electrical signal by modulatingthe high frequency current flowing therethrough. This modulated highfrequency current continues to be confined to the dominant paths definedby the bow arms and, in turn, generate an output electromagnetic signal422 that emanates from the bow arms.

[0100] Peripheral outline 406 of the antenna arrangement serves todefine further characteristics of dominant paths 430 and 432. Inparticular, outermost ends 402 and 404 of the bow arms serve not only indefining ports 408 and 410, but also to define reflector configurationswhich terminate the dominant paths. The reflector configuration of eachoutermost end is made up of first and second reflector segments 434 and436 which are positioned on opposite sides of ports 408 and 410. Thesereflector segments may comprise terminating edge segments ofnon-insulating layers 212 and 214 at the outermost ends. In this regard,it should be appreciated that the antenna configuration of FIG. 5 isillustrative of a resonant antenna configuration in which the surfacecurrents oscillate or resonate along the dominant paths. Suchcirculation of the surface currents is considered to be highlyadvantageous in either of a modulation implementation or a detectionimplementation since opportunities for the surface currents to leak outof the dominant paths are limited, as will be contrasted with prior artconfigurations in a subsequent discussion.

[0101] In the present example, each bow arm includes an elongation axisabout which the ports and reflector segments are symmetrically arranged,however, this is not a requirement so long as the resonancefunctionality of the dominant paths is not overly suppressed. In termsof design concerns, it is recognized that the width of the dominantpaths is influenced by a combination of factors at least includingmaterial properties of the bow arms and the angle of flare used in thebow arm (indicated as θ in FIG. 5).

[0102] In the instance of using assembly 400 in the emitter mode, theintegrated device emits electromagnetic radiation into the bow arms toproduce surface currents in dominant paths 430 and 432. Consequently,output electromagnetic signal 422 is produced in the absence ofelectromagnetic energy 421 incident upon the bow arms.

[0103] Turning now to a discussion considering the use of arrangement400 in the detection mode, it is initially important to understand thatthe surface current resonates in the same manner, irrespective ofwhether it is produced in a detection, mixer, emitter or modulationmode. With that in mind, the present description is limited to thoseaspects of operation which are, in fact, different in this alternativemode. In the detection mode, an electromagnetic radiation 440 isincident on the bow arms whereby to induce the surface currents inresonant paths 430 and 432. The incident electromagnetic radiation maybe within a frequency range of approximately several kHz to visiblelight and may be unmodulated, in such an instance as solar energyconversion, or modulated with any suitable information signal which isto be recovered, such as in optical communication. The surface currentsare again confined to resonant paths 430 and 432 to be routed throughthe active device at the confronting portions of the bow arms such thatthe device acts on the surface current to emit a lower frequency outputsignal into the antenna arrangement, responsive to the surface current.The emitted output may comprise a direct current in the instance ofsolar energy conversion or a demodulated signal that has been detectedas the envelope of incident electromagnetic radiation, serving as anamplitude modulated carrier. Again, the detected signal is emitted at afrequency that is sufficiently lower than the high frequency current soas to be present at least generally throughout the antenna including atports 408 and 410. A detected output signal 442 is illustrated by anarrow that extends from the detection device directly to port 410. It isto be understood that such a detected output also travels from thedetection device to port 408 but has not been shown due to illustrativeconstraints.

[0104] When assembly 400 is used in a mixer mode, incidentelectromagnetic energy 421 may include at least two differentfrequencies such as a first frequency and a second frequency. Mixingthen produces an output difference frequency as output 442.

[0105] Inasmuch as device integrated antenna 400 has been described indetail above with respect to its structure and operationalcharacteristics, attention is now directed to certain attendantadvantages. Initially, it is important to understand that each of ports408 and 410 is positioned sufficiently away from each of the resonantpaths to isolate the lower frequency signal, traveling between the portsand the active device, from the surface currents that are confined tothe resonant paths, at least from a practical standpoint. That is, theports are spaced-apart from the resonant paths sufficient to produceisolation from the surface currents. In and by itself, this isolation isconsidered to be a sweeping advantage over prior art configurations. Asa first advantage, leakage of surface currents into the ports isprevented. As a second advantage, overall efficiency is enhanced byreducing leakage currents. This latter advantage is readily understoodwith reference to using device integrated antenna 400, for example, inthe detection mode. In this context, any active detection deviceexhibits a certain conversion efficiency. Therefore, a first portion ofsurface current that is traveling through the device at a given time isdown-converted to the lower frequency. At the same time, a second,transmitted portion of the surface current travels through the devicewithout conversion, while a third, reflected portion of the surfacecurrent is reflected upon attempting to enter the device. The presentinvention is considered to provide sweeping advantages with regard tothe transmitted and reflected portions of the surface currents. Theseportions simply remain on the resonant paths of the antenna only to passthrough the device on another round trip. Thus, conversion efficiency isenhanced since the surface current may be down-converted on a subsequentround trip. In addition, the designer may choose the resonant length(i.e., the reflector to reflector length of the dominant paths) so as toshape the dominant path for maximal impedance-matching with a particulardevice.

[0106] With the foregoing advantages in mind, it is worthwhile tobriefly consider the approach of the prior art. Conventional resonantbowtie antennas generally use a center fed configuration wherein aninput or output is transferred into or taken out of the bowtie at theintersection of the bow arms. For a device integrated configuration, theinput/output port is at the bowtie intersection, co-located with theintegrated active device. The present invention considers this approachas being unacceptable, with or without an integrated active device, atleast for the reason that the resonant paths defined by the bowtie musttravel through this intersection region. Accordingly, surface currentleakage into the low frequency signal paths at the intersection point isvirtually assured. As a further disadvantage, in a device integratedconfiguration, the leakage reduces overall efficiency in either adetection or modulation mode by removing a portion of the circulatingresonant current. The present invention, in contrast, is thought tocompletely resolve this difficulty by using bow arm outermost endconfigurations, which integrate reflection segments so as to maintainresonant path oscillation, in cooperation with co-integrated ports fortransmitting an input or output signal in isolation from the resonantsurface currents. For example, if the device integrated antenna of thepresent invention is used in a detection mode, the resonating surfacecurrent has the opportunity to pass through a detection device arrangedat the innermost end of the bow arms any number of times with littleopportunity to leak out.

[0107] It is important to understand that the illustrated symmetricalconfiguration of FIG. 5 may be altered in any number of ways whileremaining within the scope of these broad teachings. For example, theports may be located at any position within the antenna assembly whereinterference with the resonant surface currents is avoided or is atleast at a tolerable level.

[0108] Attention is now directed to FIG. 6A, which illustrates anotherimplementation of the device integrated antenna of the present inventionthat is generally indicated by the reference number 500. Since antennaarrangement 500 is similar to antenna arrangement 400 of FIG. 5,descriptions of like components will not be repeated for purposes ofbrevity and the reader is referred to discussions appearing above.Antenna arrangement 500 differs, however, in the configuration of itsinput/output ports. In this example, the ports are indicated by thereference numbers 408′ and 410′, including an inset configuration withinoutermost ends 402 and 404, respectively. It should be appreciated thatantenna arrangement 500 shares all of the advantages of antennaarrangement 400 while providing still further advantages, as will bedescribed immediately hereinafter.

[0109] Turning to FIG. 6B in conjunction with FIG. 6A, a more enlargedplan view of bow arm 412 and inset port 408′ are provided forillustration of certain characteristics of surface currents 550(indicated as a plurality of arrows). It is noted that this illustrationhas been presented in a way which is thought to enhance the reader'sunderstanding with respect to flow of surface currents and is not toscale. What is clearly shown, however, is that the dominant paths canadvantageously be shaped by cutting an inset feed (port 408′) to altercurrent flow when the dominant path is considered as the collective flowdefined by the individual high frequency current arrows. Using thisrecognition, resonance and impedance matching conditions may be mademore favorable. In particular, cut-aways of a length 552 and a width 554define the inset geometry of port 408′. As another advantage, the pathtaken by the high frequency current is influenced such that interactionbetween the antenna and the device at the apex of the bow arm is mostfavorable for energy transfer into and/or out of the device.

[0110] It should be further appreciated that any port may be inset oroutset by any suitable amount so long as interference/leakage withresonant paths 430 and 432 is at an acceptable value. Moreover, theinset/outset may be thought of as zero in the configuration of FIG. 3Ahaving a straight line outermost end. Additionally, the ports in asingle device integrated antenna may have different configurations. Forexample, one port may be outset while the opposing port is inset.Variation of the inset/outset values from one bow arm to the opposingbow arm can be advantageous, for example, when the bow arms are ofdifferent sizes. For instance, where one bow arm is lengthened relativeto the other bow arm along its elongation axis, the inset may beincreased to alter the port position for the lengthened bow arm.

[0111] At this juncture, it is appropriate to note that the presentinvention, as exemplified by the embodiments of FIGS. 5 and 6A, providesa resonant bowtie antenna that is not center fed. Applicants are unawareof such a highly advantageous configuration in the prior art.

[0112] Turning now to FIG. 7, still another implementation of the deviceintegrated antenna of the present invention is generally indicated bythe reference number 600. While the configuration of antenna 600resembles that of antenna 500, its configuration, as well as operation,is different in an important respect. In particular, antenna 600includes a non-resonant configuration. As described above, in anon-resonant configuration, the paths which confine the surface currentsare referred to as dominant, rather than resonant paths. A pair ofopposing dominant paths are indicated by the reference numbers 602 and604. In order to produce this non-resonant configuration, bow arms 212and 214 are lengthened to an extent that causes surface currents thatflow in the dominant paths to decay to an insignificant level.Accordingly, there is no significant surface current to reflect uponreaching outermost ends 402 and 404. While shown in a reflectiveconfiguration using reflective edge segments 606, the outermost ends mayinclude end segments (not shown) that are configured so as not toreflect surface currents which may reach them. Sufficientnon-reflectivity, of course, may serve to reduce or eliminate the needfor elongation of the bow arms.

[0113] Still referring to FIG. 7, a pair of opposing ports are indicatedby the reference numbers 408″ and 410″. Like the ports shown in FIG. 6A,these ports remain inset within the bow arms, but appear as beingrelatively further inset, primarily due to elongation of the bow arms.It should be observed that the ports are arranged such that the surfacecurrent in dominant paths 602 and 604 travels past the ports in adirection that is generally away from the active device at the innermostends of the bow arms. Moreover, as a result of the highly advantageousconfiguration of antenna 600, the surface currents nearest the ports maystill be at significant levels, while the ports remain isolatedtherefrom. In this regard, antenna 600 shares the advantages ofpreviously described embodiments with respect to isolation, but in anon-resonant configuration.

[0114] Prior art non-resonant bowtie antennas are generally seen in whatis generally referred to as an edge fed configuration wherein the entireoutermost end of each bow arm connects to a low frequency lead. That is,the low frequency lead, proximate to the antenna, generally includes thesame width as the outermost end of the bow arm and extends outwardlyfrom the outermost end, maintaining the outermost end width for somedistance which permits the surface currents to decay to negligiblelevels. Having eliminated the surface currents to a sufficient degree,the low frequency leads extending from the bow arms are merged into asuitable transmission line. This configuration is seen, for example, inFIG. 7, page 538 of the aforedescribed article entitled Imaging AntennaArrays by David B. Rutledge, et al. [10]. The present invention, incontrast, does not require elongated edge feed leads for purposes ofsurface current decay. Such surface currents are isolated from the lowfrequency ports due to a highly advantageous physical location which is,at least potentially, between opposing dominant paths. Accordingly, amore compact configuration is provided by the present invention.

[0115] It is to be understood that the present invention, and theadvantages attributed thereto can be utilized in electromagnetic deviceapplications other than solar energy conversion devices. Theseapplications include, but are not limited to, detectors of all of theelectromagnetic frequency spectrum, including superconducting detectors,emitters, modulators, repeaters and transistors, as disclosed in theapplicants' copending U.S. patent application Ser. No. 09/860,972,Attorney Docket Number Phiar-P002, filed simultaneously with the parentapplication of the present application and incorporated herein byreference. Additionally, an external bias voltage may be applied to thenon-insulating layers in these applications to operate the device in adesired region on the I-V curve. Therefore, the present examples are tobe considered as illustrative and not restrictive, and the invention isnot to be limited to the details given herein but may be modified withinthe scope of the appended claims.

What is claimed is:
 1. An assembly comprising: a device configured forreceiving at least one input to produce an output responsive thereto; anantenna arrangement for supporting said device to transfer said input tothe device and further to transfer said output from said device suchthat the antenna arrangement supports a selected one of the input andthe output as a high frequency current and said antenna arrangementincludes a peripheral configuration which confines said high frequencycurrent to at least one dominant path within the antenna arrangement sothat the high frequency current oscillates in the dominant path and sothat the other one of the input and the output is a lower frequencysignal that is present at least generally throughout the antennaarrangement; and at least one port, within said antenna arrangement,positioned sufficiently away from said dominant path so as to isolatethe lower frequency signal at the port from said high frequency currentin said dominant path, wherein said antenna arrangement is configured tosupport said lower frequency signal having a frequency of at least oneterahertz.
 2. The assembly of claim 1 wherein said high frequencycurrent is produced responsive to an incident electromagnetic radiationthat is incident upon the antenna arrangement at a given frequency, andwherein said antenna arrangement is further configured to receive saidincident electromagnetic radiation having said given frequency selectedfrom a high frequency range including several kilohertz to severalhundred terahertz.
 3. The assembly of claim 1 wherein said port servesas an input port which receives the lower frequency signal for transferto said device as said input and an incident electromagnetic radiationis incident on said antenna as an additional input in a way whichgenerates said high frequency current such that the high frequencycurrent travels through said device and the device modulates the highfrequency current passing therethrough and back into the antennaarrangement to cause a modulated electromagnetic radiation to beradiated from the antenna arrangement, and wherein said antennaarrangement is further configured to radiate said modulatedelectromagnetic radiation having a radiation frequency selected from ahigh frequency range including several kilohertz to several hundredterahertz.
 4. The assembly of claim 1 wherein said device is an emitter,wherein said port serves as an input port which receives the lowerfrequency signal for transfer to said emitter as said input in a waywhich causes the emitter to inject said high frequency current into theantenna arrangement to cause a modulated electromagnetic radiation to beradiated from the antenna arrangement, and wherein said antennaarrangement is further configured to radiate said modulatedelectromagnetic radiation having a radiation frequency selected from ahigh frequency range including several kilohertz to several hundredterahertz.
 5. The assembly of claim 1 wherein an input electromagneticradiation is incident upon the antenna arrangement having at least afirst frequency and a second frequency to produce said high frequencycurrent in the antenna arrangement including the first frequency and thesecond frequency, wherein said device is a mixer which receives the highfrequency current to produce said lower frequency signal as a differencefrequency between the first frequency and the second frequency fortransfer to the port, and wherein said antenna arrangement is furtherconfigured to receive said input electromagnetic radiation having firstand second frequencies selected from a high frequency range includingseveral kilohertz to several hundred terahertz.
 6. In producing anassembly, a method comprising: providing a device for receiving at leastone input to produce an output responsive thereto; supporting saiddevice within an antenna arrangement to transfer said input to thedevice and to transfer said output from said device such that theantenna arrangement supports a selected one of the input and the outputas a high frequency current and said antenna arrangement includes aperipheral configuration which confines said high frequency current toat least one dominant path within the antenna arrangement so that thehigh frequency current oscillates in the dominant path and so that theother one of the input and output is a lower frequency signal that ispresent at least generally throughout the antenna arrangement; andpositioning at least one port, within said antenna arrangement,sufficiently away from said dominant path so as to isolate the lowerfrequency signal at the port from said high frequency current within thedominant path, wherein supporting said device within said antennaarrangement includes configuring said antenna arrangement to supportsaid lower frequency signal having a frequency selected from a lowfrequency range including zero to several terahertz.
 7. An assembly,comprising: a device configured for receiving at least one input toproduce an output responsive thereto; an antenna arrangement forsupporting said device to transfer said input to the device and furtherto transfer said output from said device such that the antennaarrangement supports a selected one of the input and the output as ahigh frequency current and said antenna arrangement includes aperipheral configuration which confines said high frequency current toat least one dominant path within the antenna arrangement and the otherone of the input and the output is a lower frequency signal that ispresent at least generally throughout the antenna arrangement; and atleast one port, within said antenna arrangement, at a location selectedsuch that the high frequency current travels past the port in at leastone direction that is away from said device, and which port ispositioned sufficiently away from said dominant path so as to isolatethe lower frequency signal at the port from said high frequency currentin said dominant path, wherein said antenna arrangement is configured tosupport said lower frequency signal having a frequency selected from alow frequency range including zero to several terahertz.
 8. An assembly,comprising: a device configured for receiving at least one input toproduce an output responsive thereto; an antenna arrangement forsupporting said device to transfer said input to the device and furtherto transfer said output from said device such that the antennaarrangement supports a selected one of the input and the output as ahigh frequency current and said antenna arrangement includes aperipheral configuration which confines said high frequency current toat least one resonant path within the antenna arrangement so that thehigh frequency current oscillates in the resonant path between a pair ofopposing first and second reflector configurations that are formed aspart of the peripheral outline and so that the other one of the inputand the output is a lower frequency signal that is present at leastgenerally throughout the antenna arrangement; and at least one port,within said antenna arrangement, positioned sufficiently away from eachone of said first and second reflector configurations so as to sustainreflection of said surface current in said resonant path whileconducting said lower frequency signal, wherein said antenna arrangementis configured to support said lower frequency signal having a frequencyselected from a low frequency range including zero to several terahertz.9. The assembly of claim 8 wherein said high frequency current isproduced responsive to an electromagnetic radiation that is incidentupon the antenna arrangement as an additional input at a givenfrequency, wherein said device is configured for emitting said lowerfrequency signal into the antenna arrangement at a different frequencyresponsive to the incident electromagnetic radiation, and wherein saidantenna arrangement is further configured to receive saidelectromagnetic radiation having said given frequency selected from ahigh frequency range including several kilohertz to several hundredterahertz.
 10. The assembly of claim 8 wherein said port serves as ainput port which receives the lower frequency signal for transfer tosaid device as said input and an incident electromagnetic radiation isincident on said antenna as an additional input in a way which generatessaid high frequency current such that the high frequency current travelsthrough said device and the device modulates the high frequency currentpassing therethrough and back into the antenna arrangement to cause amodulated electromagnetic radiation to be radiated from the antennaarrangement, and wherein said antenna arrangement is further configuredto receive said incident electromagnetic radiation having a givenfrequency selected from a high frequency range including severalkilohertz to several hundred terahertz.
 11. An assembly comprising: adevice configured for receiving at least one input to produce an outputresponsive thereto; an antenna arrangement including a bowtie peripheralconfiguration defining a bowtie intersection for supporting said deviceat the bowtie intersection to transfer said input to the device andfurther to transfer said output from said device such that the antennaarrangement supports a selected one of the input and the output as ahigh frequency current and said bowtie peripheral configuration confinessaid high frequency current to at least one dominant path within theantenna arrangement so that the high frequency current oscillates in thedominant path traveling through said bowtie intersection and so that theother one of the input and the output is a lower frequency signal thatis present at least generally throughout the antenna arrangement; and atleast one port, within the antenna arrangement, positioned spaced apartfrom said bowtie intersection and sufficiently away from said dominantpath so as to isolate the lower frequency signal at the port from saidhigh frequency current in said dominant path, wherein said antennaarrangement is configured to support said lower frequency signal havinga frequency selected from a low frequency range including zero toseveral terahertz.
 12. In producing an assembly, a method comprising thesteps of: providing a device configured for receiving at least one inputto produce an output responsive thereto; configuring an antennaarrangement to include a bowtie peripheral configuration defining abowtie intersection for supporting said device at the bowtieintersection to transfer said input to the device and further totransfer said output from said device such that the antenna arrangementsupports a selected one of the input and the output as a high frequencycurrent and said bowtie peripheral configuration confines said highfrequency current to at least one dominant path within the antennaarrangement so that the high frequency current oscillates in thedominant path traveling through said bowtie intersection and so that theother one of the input and the output is a lower frequency signal thatis present at least generally throughout the antenna arrangement; andpositioning at least one port, within the antenna arrangement, spacedapart from said bowtie intersection and sufficiently away from saiddominant path so as to isolate the lower frequency signal at the portfrom said high frequency current in said dominant path whereinconfiguring said device within said antenna arrangement further includesconfiguring said antenna arrangement to support said lower frequencysignal having a frequency selected from a low frequency range includingzero to several terahertz.